Inverter only producing half power

[JerryA]

My system is about 5 years old. When first installed I would see about 2000 watts max, typically less. On a hot summer day perhaps only 1100 watts. During the last 6 months I am only seeing about 500 to 700 watts. A technician has been out twice. He checked the panels, two parallel arrays, and voltage was equal on both sets. The inverter is a Fronius IG 3000. The only error code showing is the "it got dark last night" normal one. The tech thinks it is the inverter but can not replace it without an error code. Some of these inverters have two units internally. Could one have stopped without an error code? Any suggestions? - Jerry

[Ampster]

Voltage equal on the arrays? Did he check Amperage?

[inetdog]

Voltage equal on the arrays? Did he check Amperage?

The voltage could be fine with a defective cell in one panel keeping the whole string from producing much at all. If he suspects one half of the inverter, just disconnect one half of the array at a time and then move each half to the other set of terminals.

[JerryA]

Yes, he reported equal amperage from both arrays. If the array was bad then the voltage input to the inverter would be sagging under load. Didn't see that happening. The two parallel arrays are joined at the roof. Only one pair of wires coming down to the DC disconnect and then to the inverter.

[inetdog]

Yes, he reported equal amperage from both arrays. If the array was bad then the voltage input to the inverter would be sagging under load. Didn't see that happening. The two parallel arrays are joined at the roof. Only one pair of wires coming down to the DC disconnect and then to the inverter.

Not true. That is not how an MPPT input stage works. If the array is only capable of putting out half power, the maximum power voltage, Vmp, will not be any different from the situation with full array output.

[emartin00]

The only real effective way to determine if panels are functioning properly is with an IV Curve trace. OC Voltage only tells you so much.

[jflorey2]

The only real effective way to determine if panels are functioning properly is with an IV Curve trace. OC Voltage only tells you so much.

Testing Voc and Isc will tell you 99% of what you need to know. If it passes those two tests, there's very little else that can be wrong with it.

[littleharbor]

Testing Voc and Isc will tell you 99% of what you need to know. If it passes those two tests, there's very little else that can be wrong with it.

The thing is there's no load in panels when checking either Voc. or Isc. Granted these two tests will definitely weed out a malfunctioning panel in many cases. Panels will many times show fine with no load on them but they really need to be under load, and if possible when fully heated by the sun to bring out some problems.

[jflorey2]

[LEFT][COLOR=#000000][FONT=Helvetica][SIZE=13px]The thing is there's no load in panels when checking either Voc. or Isc.

Isc is tested under maximum load (short circuit.) For panel tests you just connect the two leads together and use a clamp on ammeter.

[Ampster]

The suspense is killing me. I hope we hear the final outcome.

I am happy I have Solaredge and Enphase on my installations because in both cases I can see panel level production and ought to he able to see if my Solaredge inverters are performing. One is 300 miles away but monitoring allows me to set alerts.

[littleharbor]

Isc is tested under maximum load (short circuit.) For panel tests you just connect the two leads together and use a clamp on ammeter.

My bad on the wording. Thing is Isc. isn't going to give you a working panel's results. Just like open circuit voltage , in that you can get full Voc. from a bad panel, put a load on it and the voltage can collapse if it is a bad panel. I saw lots of this with the bad BP Solar products.

[jflorey2]

My bad on the wording. Thing is Isc. isn't going to give you a working panel's results. Just like open circuit voltage , in that you can get full Voc. from a bad panel, put a load on it and the voltage can collapse if it is a bad panel. I saw lots of this with the bad BP Solar products.

Have you ever seen a panel give a good Voc and a good Isc - then collapse when a 'normal' load is placed on it? I never have. I can't even imagine how it would happen - a very high resistance connection somewhere? But that would give you a low Isc as well.

[littleharbor]

The bad BP panels had a problem with the leads lacking in strain relief They could test ok Voc and Isc but once connected and warm in the sun they would start failing, some scorching from the back of the j-box . Some worse than others, some charred, some even so hot as to shatter the glass.

[bcroe]

Have you ever seen a panel give a good Voc and a good Isc - then collapse when a 'normal' load is placed on it? I never have. I can't even imagine how it would happen - a very high resistance connection somewhere? But that would give you a low Isc as well.

I have a couple that do that. With 3 bypass diode sections, they show good open ckt voltage. But in a string,
under best sun the voltage drops to 2/3 or 1/3 of normal. It happens because one or 2 sections cannot
maintain full current under best sun. So the rest of the string forces them into bypass.

They have no problem with open circuit voltage, and a short circuit test demonstrates the good section(s)
while the weak sections go into bypass.

I have a couple of these, culled from 4 strings of no name Evil bay panels. Still trying to find a good use
for them, either run stand alone for some minor function, or set up a pair with weak sections shorted, to
replace one good panel. Bruce Roe

[jflorey2]

I have a couple that do that. With 3 bypass diode sections, they show good open ckt voltage. But in a string,
under best sun the voltage drops to 2/3 or 1/3 of normal. It happens because one or 2 sections cannot
maintain full current under best sun. So the rest of the string forces them into bypass.

They have no problem with open circuit voltage, and a short circuit test demonstrates the good section(s)
while the weak sections go into bypass.

I have a couple of these, culled from 4 strings of no name Evil bay panels. Still trying to find a good use
for them, either run stand alone for some minor function, or set up a pair with weak sections shorted, to
replace one good panel. Bruce Roe

Interesting. Thanks for the info.